We evaluated the hypoglycemic and antioxidant effects of the total alkaloids of leaves and twigs of Catharanthus roseus Linn.(CTA) in streptozotocin(STZ)-induced diabetic rats. The hypoglycemic effect was measured by blood glucose and plasma insulin level. Oxidative stress was measured in heart, liver and kidney by levels of antioxidant markers, free radical scavengers and lipid peroxides i.e. superoxide dismutase(SOD), catalase(CAT), glutathione(GSH) and thiobarbituric acid reactive substances(TBARS). Biochemical parameters, i.e. aspartate aminotransferase(AST), alanine aminotransferase(ALT), alkaline phosphate(ALP) were observed in diabetic control and treated rats. Oral administration of CTA for30 days was followed by a significant(P 0.05) decrease in fasting blood glucose and increase in insulin level as compared with untreated diabetic rats. Also it significantly(P 0.05) reduced ALT, AST and ALP. The treatment also resulted in significant(P 0.05) reductions in GSH,SOD, CAT, and decrease in TBARS in the heart, liver and kidney of diabetic rats. The results suggest that CTA can effectively normalize the impaired antioxidant status in STZ-induced diabetes in a dose-dependent manner.CTA exerted rapid protective effects against lipid peroxidation by scavenging of free radicals and reducing the risk of diabetic complications. We hypoclycemic and antioxidant effects of the total alkaloids of leaves and twigs of Catharanthus roseus Linn. (CTA) in streptozotocin (STZ) -induced diabetic rats. The hypoglycemic effect was measured by blood glucose and plasma insulin level. Oxidative stress was measured in heart, liver and kidney by levels of antioxidant markers, free radical scavengers and lipid peroxides ie superoxide dismutase (SOD), catalase (CAT), glutathione (GSH) and thiobarbituric acid reactive substances (TBARS). Biochemical parameters, ie aspartate aminotransferase AST), alanine aminotransferase (ALT), alkaline phosphate (ALP) were observed in diabetic control and treated rats. Oral administration of CTA for 30 days was followed by a significant (P 0.05) decrease in fasting blood glucose and increase in insulin level As compared with untreated diabetic rats. Also it significantly (P 0.05) reduced ALT, AST and ALP. The treatment also resulted in significant (P 0.05) reductions in GSH, SOD, CA T, and decrease in TBARS in the heart, liver and kidney of diabetic rats. The results suggest that CTA can effectively normalize the impaired antioxidant status in STZ-induced diabetes in a dose- dependent manner. CTA exerted rapid protective effects against lipid peroxidation by scavenging of free radicals and reducing the risk of diabetic complications.